Miniaturized, vibration resistant, thermally responsive electrical switch



July 26, 1966 J. DOHERTY, JR

MINIATURIZED, VIBRATION RESISTANT, THERMALLY RESPONSIVE ELECTRICAL SWITCH Filed April 15, 1964 fur/en to r,

United States Patent 3,263,049 MINIATURIZED, VIBRATION RESISTANT, THER- MALLY RESPONSIVE ELECTRICAL SWITCH John Doherty, Jr., Assonet, Mass., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Apr. 13, 1964, Ser. No. 359,028 6 Claims. (Cl. 200-138) This invention relates to thermally responsive electrical switches and more particularly to precision thermostats. Although not limited thereto, with regard to certain more specific features the thermally responsive switch of the instant invention is especially suited for use in critical aircraft and missile applications including applications in electronic and radar equipment, gyros, accelerometers,

aerial cameras, fuel pumps, servo motors, and in refrigeration de-icing and other airborne equipment.

It will be understood, however, that the thermally responsive switch of the instant invention has many other diverse applications and may be used wherever found applicable. In addition, the switch of the instant application is particularly suitable for miniaturized, hermetically sealed construction.

, Among the several objects of the invention may be noted the provision of a new and improved thermally responsive electrical switch which permits fast response and which is adapted for miniaturization so as to be conveniently insertable into small places adjacent the parts to which a temperature response is to be made by the switch; the provision of such switches which are especially adapted for hermetically sealed construction; the provision of such switches which are precise and relatively simple to calibrate; the provision of such switches which are accurate, compact, and reliable in operation; the provision of such switches which provide for improved vibration and shock resistance and which are not position sensitive; the provision of such switches which embody a minimum number of parts, are simple in construction and economicalto manufacture and assemble; and the provision of-such switches which are capable of precise operation in hostile environments.

Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction and electrical I 1; and

FIG. 3 is a plan view of a contact arm employed in the device shown in FIG. 1.

Similar reference characters indicate corresponding parts throughout the several views of the drawings. Dimensions of certain of the par-ts as shown in the drawings have been modified for the purpose of clarity of illustration.

' Referring now to the drawings particularly FIG. 1, a thermally responsive electrical switch according to the instant invention is generally designated by reference numeral 10. Switch 10 includes a cup-shaped housing or casing member 12 formed of a suitable material of high heat conductivity such as, for example, carbon steel. On its closed end portion cup-shaped casing 12 is provided with an internal annularly extending shoulder 14. Mounted in supportive, heat conductive relationship back to the opposite. position of stability. The mounting of disc 16 on shoulder 14 provides a cavity or'recess 18 in housing 12 which permits the disc 16 to snap to the position of concavity shown in FIG. 1, without striking the housing 12 and deleteriously atfecting its temperature calibration.

Mounted on the open end of cup 12 is a header assembly generally indicated by reference numeral 20. Header 20 includes a flanged plate 22 formed, for example, of a suitably weldable material. Plate 22 is mounted with its flanged edge mounting with corresponding flanges on housing 12, and is attached thereto as, for example, by heliarc welding to provide a hermetic seal for the interior of switch '10.

Embedded in and sealed to a glass sealant 26 are electrically conductive terminals 28 and 30. This glass-tometal seal for the header subassembly 20 is preferably of the so-called compression seal construction whereby the glass sealant 26 is selected to have a coefiicient of expansion less than that of plate 22 such that plate 22 on cooling shrinks around sealant 26 to provide a mechanically strong hermetic seal. It will be understood that, after the header assembly 20 is hermetically sealed to housing 12, the device may be coated with a suitable material to provide a corrosion resistance.

Cantilever mounted on the inner end of terminal 28 on one of its ends is a movable contact arm generally indicated by reference numeral 32, formed of a suitably electrically conductive, resilient material. On the other end of contact arm 32 is an electrically conductive contact 34 mounted for movement into and out of engagement with a stationary electrically conductive contact 36 mounted on the inner end of terminal 30. Contacts 34 and 36 are formed of a' suitably electrically conductive material such as, for example, silver.

Contact carrying arm 32 includes a generally centrally located aperture 39 extending through which is the re duced-diameter portion 38 of a transfer pin 40. The lower portion of transfer pin 40 abuts snap acting disc 16. Pin 40 is formed of a suitably electrically insulating material such as, for example, ceramic. Motion transfer pin 40 serves to transfer snap movement of disc 16 inthe upward direction to the contact arm 32 to move movable contact 34 into engagement with stationary contact 36.

Disposed within cup-shaped housing 12 is a cup-shaped liner member 42 formed of a suitably electrically insulating material such as, for example, ceramic. Liner 42 generally compares to housing 12 in shape. The lower portion of insulating liner 42 includes an aperture 44 in which transfer pin 40 is disposed. Transfer pin 40 interfits sufficiently loosely with apertures 44 and 38 to prevent jamming of the transfer pin in either of these apertures. The lower portion of insulating liner 42 provides an arc shield which prevents arcing and material flow from Y the contacts from reaching disc 16 and deleteriously affecting its temperature setting. Further, the entire liner member 42 provides electrical insulation of the housing 12 from the'electrical circuit through terminal 28, arm 32, contacts 34 and 36 and terminal 30 and permits the housing to be at a different potential from that circuit such as, for example, ground. 1

It will be noted that movable contact carrying arm 32 is bent at 46 such that movable contact 34 is normally biased out'of engagement with stationary contact 36. As

Patented July 26, 1966 best seen in FIG. 3, contact carrying and 32 includes slots 49'which form a central section 48; When disc 16 has snapped to its opposite position of concavity from that seen in FIG. 1, to place contacts 34 and 36 in engagement, the central portion 48'including aperture 1590f arm 32 is permitted to belly upwardly beyond the plane of arm 32due toslots 49.

It will be seen, then, that thisconstruction of arm 32 advantageously provides a" dual rate spring. In the con-- tacts openposition seen'in FIG. 1 when the bend line is at 46 spring 32 is more flexible and can be easily moved After contact engagement spring 32acts as ashorter andhence by disc 16'to move towards contact engagement.

stiffer spring and exerts a-relatively greater force tending to urge contacts 34- and 36 into engagement. It will be noted, however, thatsome of the spring action of arm 32, in the contacts closed position, transfers to its center section 48 such that the stiffening of spring 32 does not act to make deflection of arm 32 and hence transfer pin length critical.

It will-be noted that the bellying out center section 48 bends to take up creep movement'of disc 16as itcools and moves toward the contacts open position.

It will'be understood that the device is calibrated by proper selection of the-disc 16 and by selecting the proper length of pin 40.

interposed between the lower peripheral portion of line-r member 42 and the peripheral portion of disc 16 is a wave spring washer, generally indicated by reference numeral 50and'formed of a suitable, flexible and resilient material. Washer 50 has'an outer diameter which approximates that of the interior diameter, of cup-shaped housing 12 as best seen in FIG. 2. Spring washer 50 is undulated in form, the peaks being indicated at 52 and the valleys at 54. The peaks 52 engage the lower portion of liner 42 while the valleys'54'engage disc 16. The" interior diameter of washer 54) is such'that washer 50' engages disc 16 substantially only at its peripheral portion thereby avoiding 'deleteriously affecting the tempera ture setting of the 'disc'16. Spring 50 advantageously providesa biasing force tending to retain disc 16 and'the liner'42 in fixed resilient position-in housing 12. Further, the biasing force of'spring 50 urgesdisc 16 into engagement with housing 12- at 14'to thereby provideimproved thermal engagement between the'disc;16 and the heat conducting housing-12. Further, spring-t retains cup-shaped member 42 in position within cup-shaped housing '12 and prevents abradingcaused-by vibration induced relative-movementof the'housing 12and the liner 42. Further, spring'50 prevents shifting of the operating temperature of the disc due to; vibration induced relative motion of the insulating liner 42' against the disc 16. Finally, the'spring'50 prevents'abrading of the cup-shaped housing 12 by the disc due to vibration induced relative motion between the housing 12 and the disc' 16. Washer 50is preferably formedofv a material'such as stainless steel which retains itsresilien-cyover a relatively high temperature range.

Assuming that the disc 16 is mounted with its high er;- pansion side in the upper portion of'the disc as .viewedun FIG. land that its normal position of concavity is as viewed in FIG. 1, a rise in temperature will result in snap movement of the disc 16 to an opposite: position of concavity. This snap movement of the disc 16' urges the transfer pin 40 generally upwardly and pin 40, by bearing against the walls of .aperture 38, moves contact arm 32 upwardly to move movablecontact 34 into engagement with stationarycontact 36to complete the circuit frornterminal 28 to terminal 30. When disc 16'has completed. its movement to the contacts closed'position, the central portion ofcontact arm 32. has. bulged out from the plane of contact arm 32 to provide a stiff spring action urgingcontacts 34 and 36 into engagement. Thus the circuit through terminal.28, contact. arm.32, contacts 34 and 36 and terminal 30 is completed. Upon cooling of the disc 16 it snaps to its position of conmovable contact arm 32, contacts 34 will move out of engagement with stationary contact 36. It will be understood that disc 16 may have as its normal position a concavity opposite to that shown in FIG. 1. In this arrangement, the contacts wouldlbe normally closed and would open on temperature rise. It will also be understood that switch 10 iscapable of sensing temperature differential-s from either a fluid surrounding the device or through the surface of housing 12 adjacent'disc 16. It will be seen that the above-described construction advantageously provides a precision thermostat construction permitting its use in a generally hostile environment. It will also be seen that the above-described construction provides a highly vibration and position insensitive device of rugged construction.

In view of the above" it will be'seen that the several objects of theinven-tion are achieved and'other advantageous results attained.

It is to be understood'that the invention is not limited in its' application to the details of construction andphraseology or terminology employed herein is for the purpose of description and not of limitation.

As many changes could be made in the above constructions' without departing from the scope of theinvention, it is intended that all matter containedin theabove description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a' limiting sense, and'it is also intended'that the appended claims shall cover all such equivalent variations as come within the true spirit and: scope of the invention.

I claim:

1. A thermostatic electrical switch comprising in combination a housing; a pair of electrically conductive contacts mounted in the housing; a resilient contact-carrying armhaving one of the pair of electrical contacts mounted thereon for movement into and. out of engagement with the other of the contacts; a thermally responsive. snapacting member mounted in said housing; ,a. motion trans-. fer member located intermediate the. snap-acting member and the contact-carrying arm for transmitting snapmovement ofthe thermally responsive member to the contact-carrying arm-to move the movable contact into and out of engagement withthe other contact; a liner member formed of electrically insulating material having a portion thereof located generally intermediate the hous-v ing and the thermally responsivemember on the'one hand and the contacts and mounting arm on the other hand to electrically insulatev and. provide an arc-shield for the housing and the thermally responsive member; and a spring member disposed between and in engagement with each ofthe linermember andthe thermally responsive member to retain the liner and thermally responsive member in a generally resiliently fixed position Within the housing, the spring member engaging the thermally responsive member substantially only atperipheralvpon tions of the thermally responsivegmember.

2. A device asset forthiin claim 1 wherein said housing has a generally cuplike' shape and wherein .the liner member has a cup-likeshape closely conforming to the interior configuration of the housing;

3. A device as set forth in claim 2 wherein the-switch includes a header assembly which'hermetically sealsthe housingandi on which are mounted the stationary contact and themovable contact-carrying ,arm.

4. A device asset forth in claim 1' wherein the housing isformed of heat conducting material and includes ashoulder formed on aportion of its-interior surface and wherein the thermally responsive member is suppor-tively mounted on the shoulder in intimate heatconducting relationship therewith.

5. A device as set forth in claim 1 wherein the spring comprises a wave-washer. having dimensions such that it engages the thermally responsive member at a relatively small portion of its surface adjacent the periphery of the thermally responsive member and wherein substantially all of the force exerted by the wave washer is in an axial direction and is substantially evenly distributed about the periphery of the thermally responsive member.

6. A device as set forth in claim 1 wherein the resilient contact-carrying arm is cantilever mounted and includes apertures along its length which provide the spring with a dual rate of flexivity such that in the contacts-open po- 6 sition it acts as a relatively flexible spring and wherein in the contacts-closed position it acts as a relatively stifi spring.

References Cited by the Examiner UNITED STATES PATENTS 2,508,510 5/1950 Gillespie 200-138 2,752,454 6/1956 Kurz 200-138 3,023,350 2/1962 Broadley et a1 200-122 X 3,143,614 8/1964 Ege 200-113 BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

L. A. WRIGHT, Assistant Examiner. 

1. A THERMOSTATIC ELECTRICAL SWITCH COMPRISING IN COMBINATION A HOUSING; A PAIR OF ELECTRICALLY CONDUCTIVE CONTACTS MOUNTED IN THE HOUSING; A RESILIENT CONTACT-CARRYING ARM HAVING ONE OF THE PAIR OF ELECTRICAL CONTACTS MOUNTED THEREON FOR MOVEMENT INTO AND OUT OF ENGAGEMENT WITH THE OTHER OF THE CONTACTS; A THERMALLY RESPONSIVE SNAPACTING MEMBER MOUNTED IN SAID HOUSING; A MOTION TRANSFER MEMBER LOCATED INTERMEDIATE THE SNAP-ACTING MEMBER AND THE CONTACT-CARRYING ARM FOR TRANSMITTING SNAPMOVEMENT OF THE THERMALLY RESPONSIVE MEMBER TO THE CONTACT-CARRYING ARM TO MOVE THE MOVABLE CONTACT INTO AND OUT OF ENGAGEMENT WITH THE OTHER CONTACT; A LINER MEMBER FORMED OF ELECTRICALLY INSULATING MATERIAL HAVING A PORTION THEREOF LOCATED GENERALLY INTERMEDIATE THE HOUSING AND THE THERMALLY RESPONSIVE MEMBER ON THE ONE HAND AND THE CONTACTS AND MOUNTING ARM ON THE OTHER HAND TO ELECTRICALLY INSULATE AND PROVIDE AN ARC-SHIELD FOR THE HOUSING AND THE THERMALLY RESPONSIVE MEMBER; AND A SPRING MEMBER DISPOSED BETWEEN AND IN ENGAGEMENT WITH EACH OF THE LINER MEMBER AND THE THERMALLY RESPONSIVE MEMBER TO RETAIN THE LINER AND THERMALLY RESPONSIVE MEMBER IN A GENERALLY RESILIENTLY FIXED POSITION WITHIN THE HOUSING, THE SPRING MEMBER ENGAGING THE THERMALLY RESPONSIVE MEMBER SUBSTANTIALLY ONLY AT PERIPHERAL PORTIONS OF THE THERMALLY RESPONSIVE MEMBER. 